This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-203050, filed Jul. 16, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a method of forming a fine pattern, particularly, to a pattern forming method for forming a pattern of, for example, LSI by exposing an original plate such as a photomask to light. The present invention also relates to a light exposure apparatus for working the pattern forming method of the present invention.
In a photolithography technology for transferring a pattern of a mask onto a sample such as a wafer, it is ideal for the mask not to have a defect. The mask of this kind is manufactured by preparing a mask blank free from a defect or having a defect smaller than a predetermined value, carrying out a pattern forming process, and performing a defect inspection and repair to eliminate the defect in a manner to satisfy the defect supervising standard.
Where the mask blank is not free from a defect, the frequency of the defect occurrence is increased, leading to an increased defect inspection-repair treatment. Where the repair accuracy is insufficient, it is necessary to manufacture again the mask by using a new mask blank. In this case, the defective mask blank, which is costly, must be discarded. When the defect derived from the mask blank takes place on the contour portion of the pattern, it is large possibility to be the one which is not to be repaired.
In recent years, the demands for the defect level of the mask blank have become severer and severer in accordance with miniaturization of the pattern so as to make the manufacturing technology of the mask blank markedly difficult and to invite an increase in the manufacturing cost. Also, in the reflection type mask blank using a multi-layered film, the repair technology itself has become difficult and the kinds of the defects that cannot be corrected are on the increase.
As described above, if a defect is present in a substrate that is to be exposed to light such as a mask blank, the mask prepared by forming a pattern on the substrate is caused to bear a defect. If the pattern is transferred onto, for example, a wafer by using the mask, the manufacturing yield is lowered by the influences given by the defect. Also, it is very difficult to prepare a mask blank perfectly free from a defect, and the utilization of the mask blank is markedly lowered if the mask blank having a defect is not used.
The problems described above are prominent in the case of using a costly material such as a mask blank as a substrate that is to be exposed to light and in the case of transferring a pattern onto a sample such as a wafer by light exposure.
An object of the present invention, which has been achieved in view of the situation described above, is to provide a pattern forming method that permits forming a pattern while avoiding a defective portion of a substrate that is to be subjected to light exposure so as to improve the manufacturing yield and to effectively utilize the substrate such as a mask blank.
Another object of the present invention is to provide a light exposure apparatus for easily working the pattern forming method of the present invention.
According to a first aspect of the present invention, there is provided a pattern forming method, in which a desired pattern is exposed on to a surface of a substrate to form a pattern on the substrate surface, comprising the steps of:
detecting a defect on the substrate surface;
analyzing the mutual positional relationship between the detected defect and a pattern to be formed on the substrate surface; and
based on the result of the analysis, correcting the pattern position in the step of pattern exposing on to the substrate surface in the pattern.
According to a second aspect of the present invention, there is provided a pattern forming method, in which a main surface of a mask blank used for preparation of a photomask is exposed in a desired pattern to form a mask pattern on the mask blank, comprising the steps of:
forming position measuring marks on at least two points on a main surface of the mask blank;
detecting a defect on the main surface of the mask blank and obtaining defect analysis data including at least the kind of the defect and the position of the defect relative to the position measuring marks;
comparing the obtained defect position with the relative position of the mask pattern that is to be formed on the mask blank so as to select the mask arranging position relative to the mask blank; and
measuring the position measuring mark to calculate the light exposure position and applying an exposure treatment to the selected position.
In the present invention, it is desirable to correct or select the pattern arranging position such that a defect is not located in a pattern edge.
The mask blank comprises a transparent substrate and a light-shielding film formed on the transparent substrate, and the defect comprises a black type defect and a white type defect. It is desirable to select the pattern arranging position such that the black type defect is buried in the light shielding film pattern and the white type defect is positioned in a pattern opening that is surrounded by the light shielding film pattern.
Further, according to a third aspect of the present invention, there is provided an exposure apparatus, comprising:
means for exposing a substrate surface in a desired pattern;
means for detecting a defect on the surface of the substrate;
means for analyzing the mutual positional relationship between the defect detected by the detecting means and a pattern that is to be formed on the surface of the substrate; and
means for correcting the pattern position in the step of exposing the substrate surface in the pattern based on the result of the analysis.
According to the present invention, a defect on a surface of a substrate that is to be exposed to light is detected in advance and the pattern position in the step of light-exposing the pattern to be formed on the substrate is corrected based on the kind, position, etc. of the defect. As a result, it is possible to perform a pattern formation in a manner to avoid the defective portion of the substrate, making it possible to manufacture efficiently the mask or the like that is free from a defect or in which an influence of a defect does not appear.
To be more specific, a defect in a substrate itself is accepted, and the defect is made substantially invisible after formation of a pattern by light exposure. For example, in the case of a mask blank having a light shielding film formed on a transparent substrate, a black type defect is buried in the light shielding film pattern, and a white type defect is exposed to a pattern opening in which the light shielding pattern is not present so as to make these defects invisible when a mask is prepared. Also, if the defect is not positioned in a contour portion of the pattern, the defect can be corrected easily by, for example, a laser repair.
In the present invention, the light exposure apparatus itself is provided with a mechanism for detecting a defect in a substrate that is to be exposed to light, making it possible to perform the defect detection, the pattern position correction and the patterned light exposure without moving the substrate among different apparatuses. It follows that a mask that is not affected by a defect can be manufactured easily.
As described above, the present invention makes it possible to form a pattern in a manner to avoid a defective portion of the substrate, leading to an improved manufacturing yield and an effective utilization of the substrate such as a mask blank.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.